What Are the Signs of Over-extracted Pour-Over Coffee? What Causes Over-extraction in Pour-Over Coffee?

On your pour-over coffee journey, you've likely encountered this situation: everything seems perfectly under control during the pouring process, but as the coffee in the filter begins its free fall, you become tense, thinking "Why is it flowing so slowly? Hurry up! It's going to over-extract. Should I stop the flow? What should I do?!"

What's Really Happening When Coffee Flows So Slowly?

You've double-checked your flow parameters before brewing, stayed completely focused during pouring, and everything seemed normal throughout the process - all according to plan. So why, in the end, does the drainage speed surprisingly slow down?

Many coffee enthusiasts immediately think the grind size is wrong, after all, slow flow must be related to grind size. Indeed, if you frequently read FrontStreet Coffee's articles, you know that FrontStreet Coffee judges grind size based on the pass-through rate of a #20 standard sieve.

For example, when brewing pour-over coffee, FrontStreet Coffee uses a grind size that passes 80% through a #20 standard sieve - meaning when calibrating with 10g of coffee grounds, we use the grind setting that allows 8g to pass through. In other words, whether it's 0.8mm or 0.3mm, any coffee particles smaller than 0.85mm will pass through the #20 sieve.

This is where the quality of the grinder comes into play. Taking the EK-43s as an example, when sieved through multiple different mesh sizes, at the setting where 80% passes through the #20 standard sieve, particles larger than 0.85mm account for 20%, particles between 0.5-0.85mm account for 60%, particles between 0.35-0.5mm account for 16%, and particles smaller than 0.35mm account for 4%. This represents a grinder with relatively uniform grinding.

However, when using another brand's grinder and sieving through different mesh sizes, at the same setting where 80% passes through the #20 standard sieve, particles larger than 0.85mm account for 20%, particles between 0.5-0.85mm account for 50%, particles between 0.35-0.5mm account for 18%, and particles smaller than 0.35mm account for 12%. Moreover, visually observing particles larger than 0.85mm, the chunks ground by the other brand's grinder are larger than those from the EK. Therefore, different grinders show differences in grinding uniformity.

To put it simply, the more uniform the grind, the better the extraction. The more uneven the grind coarseness, the worse the extraction, specifically manifesting as clogging from fine particles even at the same calibrated grind setting. This is why most beginners feel helpless when they see the flow rate slow down at the end, fearing over-extraction.

A Side Note: Why Are Beginners So Afraid of Over-Extraction?

Because the bitter and complex flavors from over-extraction are very unpleasant, these flavors are more repulsive than under-extraction. Over-extraction basically occurs when water soaks coffee grounds for too long, which is why many beginners feel anxious when they see water taking too long to drain.

So what duration counts as "too long"? For a normal pot of pour-over coffee, 1 minute 40 seconds to 2 minutes 20 seconds is a reasonable extraction time, with most concentrating between 1 minute 50 seconds to 2 minutes. When the time exceeds 2 minutes and the water hasn't completely drained, there's a risk of over-extraction. A few seconds over might be acceptable, but if it exceeds 10 seconds or more, for those with limited brewing experience, this constitutes over-extraction.

FrontStreet Coffee wants to say that you must experience over-extraction first to gain experience. Only then will your judgments be more accurate next time. Excessive time, under normal circumstances, does indeed produce unpleasant flavors. This is still based on the cause of time extension due to excessive fine particles.

In fact, excessive fine particles aren't the only cause of slow drainage. There are many other reasons, such as different filter cups causing different flow rates, which many enthusiasts already understand, so I won't elaborate. Another factor is the nature of the beans themselves. Careful enthusiasts will certainly notice that some beans drain quickly during brewing, while others drain very slowly, as if clogged. This is related to the hardness of the beans.

For example, Panama Geisha coffee beans have relatively hard bean density and light roast degree, resulting in lower water absorption efficiency - making it difficult to form a hamburger-like bloom. High density also makes them sink easily, so when brewing Geisha coffee, very little coffee powder floats on the surface. Due to the coffee grounds sinking, drainage becomes slower. The extraction time used is correspondingly longer, around 2 minutes to 2 minutes 30 seconds. However, this is not over-extraction.

Therefore, many beginners apply one coffee bean's brewing formula to another bean. When the bean properties are similar, it might work, but when two beans differ significantly, it becomes difficult to make correct judgments.

Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473